Braidless side break switches



March 26, 1957 y R. KLEB BRAIDLESS SIDE BREAK SWITCHES 2 Shee'ts-Sheet 1 Filed Dec. 16, 1955 ,Q bm,

March 26, 1957 R. KLEB 2,786,923

BRAIDLESS SIDE BREAK SWITCHES File` Dec. 16, 1955 2 Sheets-Sheet 2 BLESS SIDE BREAK SWITCHES Robert Kleb, Downers Grove, Ill., assignor to H. K. Porter Company, Inc. of Pittsburgh, Chicago, Ill., a corporation of Pennsylvania Application December 16, 1955, Serial No. 553,517

6 Claims. (Cl. 200-170) The present invention relates to improvements in s ide break switches and the like, and particularly, to an improved electrically conductive swivel connector for .side break switches, which connector accommodates ehmlnation of the braid conductor normally required between the blade and terminal pad of a side break switch.

A side break switch, in basic form, comprises a pair of spaced parallel insulator stacks, at least one of which is rotatable, a switch blade secured to the rotatable insulator stack for arcuate movement in a plane generally normal to the stack axes, and contact means carried by the other insulator stack to be engaged by the blade to close the switch. To connect the blade and contact to the terminal ends of the line with which the switch is to be associated, terminal pads are provided, but separate supporting insulators are not provided for the pads, so that at least the terminal pad for the blade must be supported, directly or indirectly, by the rotatable insulator stack. Yet, the terminal pad cannot rotate with respect to the line, and thus, must be mounted for rotation with respect to the insulator stack. Moreover, the rotatable connection must not impose a substantial friction load between the pad and stack, for the line would then be required to support the load. Because of this latter .requirement, known rotary electrical connectors for h1gh capacity switches and the like have proven totally unsatisfactory for commercial use on side break switches. Accordingly, it has been customary heretofore to provide a low friction mechanical connection between the terminal pad and rotatable insulator and to utilize, despite the known objections thereto, a slack length of braid conductor electrically to connect the terminal pad and switch blade. l

It is an object of the present invention to provide 1mproved, and commercially practical, braidless side break switches. More specifically, it is an object of the invention to provide an improved electrically conductive swivel connector for side break switches and the like, which connector is particularly adapted for high capacity installations, to eliminate the necessity heretofore existent Jfor a braid conductor or the like between the terminal pad and switch blade.

Another object of the invention is to provide an improved electrically conductive swivel connector for side break switches and the like incorporating the known principles and advantages of high pressuresmall area contact.

A further object of the invention is the provision of an improved electrically conductive swivel connector for two conductors in switches and the like including a novel combination of cooperating contact members and antltfriction bearings therefor presenting exceedingly little frictional resistance to relative rotation of the two conductors.

A still further object of the invention is the provision of an improved electrically conductive swivel connector attaining the objects set forth above, and at the same time, being of such sturdy construction as to constitute the sole ited States Patent ice connection between the two relatively movable conductors.

An additional object of the present invention is the provision of an improved swivel connector, and improved braidless side break switches, of compact, eicient and highly economical construction.

Other objects and advantages will become apparent in the following detailed description of preferred embodiments of the invention.

Now, in order to acquaint those skilled in the art with the present invention, I shall describe, in connection with the accompanying drawings, two preferred embodiments of side break switches formed in accordance with the present invention, and a preferred embodiment of the swivel connector of the invention.

In the drawings, wherein like reference numerals indicate like parts:

Figure l is a plan view of a braidless side break switch formed in accordance with the invention;

Figure 2 is a side eleva-tion of the switch shown in Figure l;

Figure 3 is a plan View of the braidless side break switch of the center breakttype, involving two rotatable insulators and switch blades, formed in accordance with the present invention;

Figure 4 is a side elevation of the switch shown in Figure 3;

Figure 5 is a plan View, on an enlarged scale, of a portion of a switch including my improved swivel connector; and

Figure 6 is a side view, partly in elevation and partly in section, of the apparatus shown in Figure 5, the view particularly showing my improved swivel connector in section.

Referring now to the drawings, and particularly to Figures 1 and 2, I have shown a side break switch of a generally standard type as formed in accordance with the present invention. As shown, the switch comprises a pair of spaced parallel insulator stacks 10 and 12 mounted on a common base 14. The insulator stack 10 is fixed to the base 14 and at its upper end carries a laterally open stationary contact 16 including vertically opposed contact members 18, and a fixed terminal pad 20. The contact members 18 extend at an inclination to the longitudinal axis of the switch, and the contact 16 includes a stop 21 aligned with the axis of the switch to limit insertion of a switch blade between the contact members. The insulator stack 12 is mounted on the base 14 for rotation about its own axis and includes a downwardly depending extension 22 for attachment of an operating crank or the like. At its upper end, the stack 10 carries a bracket 24 which extends angularly away from the axis of the stack 12 toward the stack 10. The bracket 24, at its outer end, lixedly carries a main switch blade 26, the blade extending perpendicular to the axis of rotation of the insulator 12 and including an end portion 28 proiecting rearwardly over the stack 12. Adjacent its rearward end, the blade 26 pivotally supports a terminal pad 30, and adjacent its opposite en-d, pivotally supports a knee blade 32, which pivotal supports or swivel connectors, as indicated generally at 34 and 36, respectively, will be explained in greater detail hereinafter. The knee blade 32 is mounted on the blade 26 for pivotal movement in a predetermined arc from a position in longitudinal alignment with the blade 26, as is shown in solid lines in Figure l, to a position wherein the knee blade is inclined in the direction ot the contact 16 from the axis of the blade 26 at an angle of approximately 45, as is shown in dotted lines in Figure 1. At its outer end, the knee blade 32 includes an enlarged portion 38to be received between the contact members `18 to close the switch. t

The switch blade of the side break switch shown -in Figures 1 and 2 is thus comprised of the blade members 26 and 32, and is secured to the rotatable insulator 12 for arcuate movement in a plane normal tothe axes ofV the insulator stacks 10 and 12. Speciiically, the blade, 26 is movable in anV arc of substantially 90 fromthe switch closed position shown `in solid lines in Figure 1, to the switch open position shown in dotted lines. Asiuovement in the switch opening direction commences, the blade 26' is moved arcuately away from the contact 16, but the knee blade 32 is held by the contact members 1S, whereupon the knee blade 32 pivots within the contact and about its pivotal support 36V on the blade 26, until the knee blade attains substantially its maximum degree of inclination to the blade 26. In such position, the blade 32 is substantially aligned with the Contact members 18, so that further rotation of the stack 17, results in longitudinal withdrawal of the contacting portion 3S of the knee blade from the contacts 1S, with the advantageous results known in the art. Thereafter, as the stack 12 is rotated to complete a 90 arc of movement, the knee blade 32 is swung away from the contact 16, with the blade 26, to open the switch. Upon rotation of the stack 12 in the opposite direction to close the switch, the movements of the blade parts occur generally in reverse sequence, with the additional factor that the stop 21 on the contact 16 limits insertion `of the knee blade 32 into the contact members, denes the position generally at which relative movement between the blades 26 and 32 commences, and denes the fully closed position of the switch, as is shown in Figure 1.

In use .of the switch, the terminal pads 2i.) and 3) are xed to line terminals to connect the switch in series with the line to be controlled thereby. As shown, the pad Ztl is xed to the contact 16 and stack 1t?, so that no particular problem arises with respect thereto. However, the pad 30 has no xed point of support, and to provide a separate stack to support the same would be exceed# ingly wasteful. Yet, the pad Sti must maintain a substantially fixed position for proper line connection, despite the fact that the only anchor for the pad is the `line itself. in View of the facts that the line must be maintained substantially stationary, and that substantial force must not be transmitted to the line, sin-ce it would normally result in line movement or undue stress thereon, it is apparent that the pivotal support or swivel connection 34 must not transmit any substantial `degree of force to the pad 3i) upon rotation of the stack 12 and switch blade. in fact, the swivelV connection 35i must be substantially frictionless to avoid transmission of force to the .pad 30 upon arcuate movement of the blade. Yet, as pointed out hereinbefore, this same connection, according to the present invention, constitutes the point of electrica-l connection between the blade and pad and the connection must be capable of carrying the ele-ctrical load on the line. The pivotal support or swivel connection 36 between the blades 25 and 32 must also meet these conicting requirements, although this connection is not quite so critical as the connetcion 34.

The same problems'as outlined above in regard to the swivel connection 34 exist in center break switches, with the further requirement that two such connections be provided. In Figures 3 and 4, I yhave shown a center break type of side break switch formed in accordance with the present invention, the switch comprising a. pair of rotatable insulator stacks 50 and 52 mounted on a common base 54 in spaced parallel relation. Both stacks include a downwardly depending extension for attachment of an operating crank or the like. At its upper end, the insulator stack 50 carries a contact blade 56 including a'blade portion 57 and vertically opposed spring biased contact members 58 secured to the .outer end ofthe blade portion. The blade is secured to the stack S by an inclined bracket 59, similar to the bracket 24, and includes a portion 61 projecting rearwardly over the stack. Adjacent its rearward end, the blade 56 pivotally supports a terminal pad 60, the pivotal support or swivel connection of the pad to the blade being indicated generally at 76. The insulator stack 52, at its upper end, carries a bracket 64 similar to, but reversed from, the bracket 59, which bracket 64 tixedly secures a switch bla-de 66 to the stack 52. The blade 66 includes an yend portion 68 projecting rearwardly over the stack 52, and adjacent its rearward end pivotally supports al terminal pad 70, the pivotal support or swivel connection of the pad'to the blade being indicated at 74. Adjacent its opposite end, the lblade 66 is curved outwardly to define a portion 78V to be inserted between the contact members 58 to close the switch, the contact me1nbers 58 being disposed at an inclination to the longitudinal axis of the switch to cooperate with the portion 7S of the blade 66.

In use, the terminal pads 6) and 7G are connected to the line terminals, and both stacks 59 and 52 are simultaneously rotatable to open and close the switch. Speciiically, the blades 56 and 66 are arcuately movable in a common plane normal to the stack axes in opposite directions and through arcs ofv substantially from the closed position shown in solid lines to the open position shown in dotted linesV in Figure 3. To etect simultanc` ous and equal rotation of the two stacks in opposite directions, and yet to require Ionly a single operating crank onv the depending extension of one or the other of the two stacks, the stacks are interconnected lby means of crank and link means indicated generally at Si?. As shown, the means di) comprises a crank 82 secured to 'the shaft of the insulator stack 50 and extending to one side of thc switch, a similar crank S4 secured to the shaft of the insulator stack S2 and extending to the opposite side of the switch, and a cross link 86 pivotally connected to said cranks at its ends, so that rotation of one stack in one direction automatically effects rotation of the other stack in the opposite direction.

As will be appreciated from the foregoing discussion of the swivel connector 34, the swivel connections 74 and 76 of the center break switch are both required to support the terminal pads 60 and 70 in such manner that very little force is transmitted to the pads upon rotation of the blades 56 and 66, and yet, areboth required to constitute an eliicient, load carrying electrical connection between the respective pads and blades.

Referring now to Figures 5 and 6V, Vl have shown in detail a preferred embodiment of the swivel connector of the present invention, which connector is particularly adapted to comprise the connections or pivotal supports 34, i4 and 76 referred to 'hereinbefora and the pivotal support or connection 36 as well. By way of example, the connector is shown and described in connection with the pivotal support 34 of the switch shown in Figures l and 2, wherein the switch includes the bracket 24, the switch blade 26 having an end portion 28, and the terminal pad 30.

As shown, the switch blade comprises a tubular conductor provided at its rearward end with portions 192 of increased wall thickness, which portions are provided with opposed slots within which a solid reenforcing bar 104 is intimately fitted, the bar being secured in the blade by a bolt 106 or the like, and the bracket 24 being secured to the reenforced portion of the blade by bolts 198 or the like. Directly above the insulator stack, or the portion of the bracket to be secured to the stack, the portions 162 of the blade are provided with aligned cylindrical bores 110 which are aligned with the axis of rotation of the insulator stack, the bracket and theblade. The bar 104 is not bored, so that the resultant effect is the provision of opposed bores in opposite sides of the switch blade. In the bottom of each bore, i. e., in the opposite sides of the bar 104 in alignment with the bores, a silver contact inlay 112 is provided to insure optimum electrical interchange, as will become apparent as the description proceeds.

At one end thereof, the terminal pad (or the inner end of the knee blade in the case of the connector 36) is bifurcated, the bifurcations 114 thereof extending in spaced parallel relation to one another perpendicular to the axis of rotation of the insulator and the bracket. As shown, the switch blade extends between the bifurcations 114, in parallel relation thereto, and terminates within the same. Each bifurcation of the terminal pad (or knee blade) is provided with an aperture therethrough, the apertures being aligned with one another, with the bores 11i) and with the axis of rotation of the insulator and bracket. A cylindrical contact 116 is secured within, suitably threaded into, each aperture and includes a portion extending into and freely received within the adjacent bore 110 in the blade. Each contact 116 is provided with a convex outer end to engage substantially solely at a point in the bottom of the respective bore 110 with the respective silver contact 112, which points of contact are aligned axially with the said bores and apertures, and thus with the axis of rotation of the insulator stack and bracket. Each contact 116 is also provided with a circumferential groove 118 in the portion thereof received within the respective bore 110, and a plurality of ball bearings 12d are positioned in each groove 118 to bear against the contact and the wall of the cylindrical bore, thus to mount the contacts 116 in the bores in the blade for rotation, and also for such axial movement as may be necessary. The cylindrical bores 110, and the circumferential grooves 118, may be formed and finished in any suitable manner to afford a smooth bearing surface engageable with the ball bearings 120. To shield the bores, the bearings and the contacts from entry of dust, moisture and other contaminants, seals 122 are provided, the seals being in the form of dished spring washers having a relatively weak spring characteristic. The springs are confined, respectively, between the inner surface of the respective bifurcation 114 and the adjacent surface of the switch blade. Specifically, each spring engages at its convex surface, adjacent its inner edge, against the adjacent bifurcation and around the contact 116 and at its outer edge engages the portions of the blade around the bore 110, thus to seal the bore.

The terminal pad (or knee blade) also includes spring means for forcibly biasing the bifurcations 114 toward one another, thus to exert a substantial compressive force on the contacts. To this end, a headed tie rod 124, suitably in the form of a bolt and nut, is extended between and through the bifurcations 114 in spaced parallel relation to the axis of the bores 110 and apertures, and in spaced relation to the rearward end of the switch blade, and a spring 126 is conned between each head of the tie rod and the exterior surface of the adjacent bifurcation. Preferably, each spring 126 comprises a pair of opposed spring cup washers, suitably formed of Phosphor bronze. Rearwardly of the springs and bifurcations, a lug pad 128 is formed integrally with the bifurcations to accommodate attachment to the pad of a line terminal.

To insure optimum conductivity, the terminal pad, switch blade and reenforcing bar 104 are preferably formed of copper or other metals or alloys havinghigh conductivity characteristics. The Contact inlays 112 are preferably formed of silver, and the contacts 116 may be formed of copper, silver, or a `copper base having a silver tip portion. The springs 126 force the contacts 116 into high pressure engagement with the contact inlays 112 on the blade, so that efficient electrical connection, capable of carrying line load, is effected between the blade and contacts even though contact area comprises only two points. Moreover, point contact in such manner not only affords the known advantages of high pressure-small area contacts, but also offers exceedingly little resistance to relative rotation of the contacts and the blade. The anti-friction ball bearing means serve, in conjunction with the point contacts, rotatably and slidably to support the contacts in the blade, likewise with exceedingly little resistance to relative rotation.

Due to the disposition of the contacts and bearings iri axial alignment with the axis of rotation of the insulator, bracket and blade, movement of the terminal pad with respect to the remainder of the structure is purely rotational, and the contacts constitute the axis of rotational movement. Thus, the contact assembly comprises both the electrical and the mechanical connection between the blade and terminal pad, in which connection mechanical resistance to relative rotation is exceedingly low, thereby to meet the requirements of the art and satisfy the objects set forth hereinbefore.

Moreover, the construction of the `swivel connector is so sturdy as to eliminate any necessity for mechanical connection of the terminal pad to the insulator stack, so that the contacts and bearings engaging in the bores in the blade constitute the sole connection of the blade and terminal pad. Y

As is to be `appreciated from the foregoing, the swivel connection at 34 in the switch shown in Figures 1 and 2, and the swivel connections at 74 and 76 in the switch shown in Figures 3 and 4, are effected exactly in the manner shown in Figures 5 4and 6, while the swivel connection lat 36 in the switch 1shown in Figures l and 2 is effected with exactly the same assembly, las shown in Figures 5 and 6, of the blade end, the contacts, the bearings .and the bifurcations of the end portion of the knee blade 32. Other similar electrical connections may likewise be effected with the said assembly.

While I have shown and described what I regard to be preferred embodiments of my invention, it will be appreciated that various changes, rearrangements and modifications may be made therein without departing from the scope of the present invention, as defined by the appended claims.

I claim:

l. An electrically conductive swivel connector for side break switches and the like, comprising -a first conductor having a bifurcated end portion, the bifurcations of said first conductor having aligned apertures therein, a second conductor including an end portion projecting between the bifurcations of said first conductor, said end portion of said second conductor having aligned bores in the opposite sides thereof [aligned with the apertures in the bifurcations of said first conductor, a contact mounted in the aperture in each bifurcation of said first conductor, said contact-s ext-ending axially `into said bores in said second conductor :and having clearance relative to the side wlalls of said bores, said contacts each having an outer eind engaging said second conductor at the bottom of the respective bore solely at a point aligned with the axis of said bores and said apertures, an anti-friction bearing positioned in eac-h bore and rotatably mounting the respective contact therein for rotation about t-he axis of said bores and said apertures, yand spring means biasing said bifurcations of said first conductor toward one another thus to exert a compressive force on said contacts to maintain high pressure, low friction, point contact between said second conductor and said contacts, said point contacts and said bearings rotatably mounting said first conductor on said second conductor, said contacts and said bearings comprising the sole connection between said conductors and connecting said conductors both mechanically land electrically.

2. An electrically conductive swivel connector for side break switches and the like, comprising a first conductor having a bifurcated end portion` the bifurcations of said first conductor having aligned apertures therein, a second conductor including an end portion projecting between the bifurcations of said first conductor, said end portion of said second conductor having aligned cylindrical bores in the opposite sides thereof aligned with the apertures in said bifurcations, a. cylindrical contact mounted in the aperture in each bifurcation, said cylindrical contacts being freely positioned respectively in -said bores in said second conductor and each having an outer end engaging the second conductor at the bottom -of the respective bore solelytat a point aligned with the axis of said bores and apertures, each of said cylindrical contacts, having a circumferential groove in the portion thereof positioned in the respective bore, la plurality of ball bearings positioned in the groove of each cylindrical Contact and bearing against the cylindrical wall of the respective bore rotatably tomount said cylindrical contacts in said bores, and spring means on said rst conductor exerting a compressive fonce on said bifurcations and thus on said cylindrical lcontacts to maintain high pressure, low friction, point contact between said conductors, said point contacts and said bearings rotatably connecting said conductors and comprising the sole connection therebetween. 3,. An,l electrically conductive swivel connector for side break switches land the like, comprising a first conductor having a bifurcated end portion, the bifurcations of said first4 conductor having aligned apertures therein, a second conductor including yan endA portion projecting between said bifurcations, said end portion of said second conductor having aligned bores in the opposite sides thereof alignedwith the apertures in said bifurcations, a. contact mounted in the aperture in each bifurcation, said confacts beingfreely positioned respectively in said bores in said second conductor and each having an outer end engaging the second conductor at the bottom of the respective bore solely at 1a point aligned with the axis of said bores and apertures, anti-friction bearing means rotatably mounting said contact-s in said bores, a headed tie rod extending between and through said bifurcations in spaced parallel relation to the axis of said bores and apertures and, in spaced relation to the end of said second conductor, and a pair of opposed spring cup washers confined between the lhead at each end of said tie rod and the outer side of the .adjacent bifurcation to exert a compressive. force on said bifurcations and thus on said contacts to maintain high pressure, low friction, point Contact between said conductors, said point contacts and said bearings rotatably connecting said conductors and comprising the sole connection therebetween.

4. ln a side break switchyhaving a rotatable insulator,l

a switch blade carried by the insulator and a terminal pfad to be supportedV for rotation with respect to the insulator and blade `and' to be electrically connected to the blade, the improvement comprising the provision of a terminal pad having a bifurcated end portion, the bifurcations of said pad having aligned 4apertures therein aligned with the `axis of rotation ofthe insulator, a switch blade including an end portion projecting4 over the insulator between .and parallelV to the bifurcations of said pad, a bracket secured to said blade in spaced relation to said en d portion land connecting said blade to the insulator, said end portion of said switch blade having aligned cylindrical bores in the opposite sides thereof aligned withy the axis of rotation of the insulator and the apertures in said bifurcations, cylindrical `Contact mounted in the aperture in each bifurcation of said pfad, said cylindrical contacts being freely positioned respectively in said bores in said blade and each having, a convex outer end engaging the blade at the bottom of the respective bore solely at a point aligned with the axis ofrotfation of the insulator, each of said cylindrical contacts Ihaving a circumferential groovef in the portion thereof positioned in the respective bore, a plurality of ball bearings positioned in the` groove in each cylindrical contact and bearing against the cylindrical wall of the respective bore rotatably to mount said cylindrical `contacts in said bores, a headed tie rod extending between and through said bifurcations of said pad in spaced parallel relation to the axis of rotation of the insulator and in spaced relalion to the end of said blade, and a pair of opposed spring cup washers confined between the head at each end of said `tie rod and the outer side of the adjacent bifurcation to exert a compressive force on said bifurcations andt'hus onY said cylindrical contacts to maintain high pressure, low friction, point contact between said blade and said contacts, said point contacts and said bearings rotatably mounting -said pad on said blade and comprising the sole connection of said pad to said blade and insulator.

5,. VAn electricadly conductive swivel connector for side break switches and the like, comprising a first conductor having avbifurcated end portion, the bifurcations of said first conductor having aligned apertures extending perpendicularly therethrough, a second conductor including an end portion projecting between and parallel to the bifurcations of said first conductor, said end portion of said second conductor having aligned cylindrical bores in the opposite sides thereof aligned with the apertures in the bifurcations of said first conductor, a silver contact on said first conductor in the bottom of each of said bores, a cylindrical contact of a diameter less than that of said bores mounted in the aperture in each bifurcation of said rst conductor, said cylindrical contacts being freely positioned respectively in said bores in said second conductor and each having a convex outer end engaging the respective silver contact solely at a point aligned with the axis of said bores and said apertures, each of said cylindrical contacts having a circumferential groove in the portion thereof positioned in the respective bore, a pluralityof bail bearings positioned in the groove in each cylindrical Contact aridabearing against the cylindrical wall of the respective bore rotatably and slidably 'to mount said cylindrical contacts in said bores, a seal for each of said bores including an annular spring disposed between the,respectivetbifurcation of said rst conductor and the cylindrical contact mounted therein and th'e adjacent surfaceA of said` second conductor surround-ing the adjacent bore to close tthe bore and seal the cylindrical contact and the ball bearings therein, a headed tie rod extending between and through said bifurcations of said first conductor in spaced parallel relation to the axis of said bores and said apertures and in spaced relation to the end of said second conductor, and a pair of opposed spring cup washers conned between the head at each end of said tie rod and the outer side of the adjacent bifurcation to exert a compressive force on said bifurcations and thus on said cylindrical contacts to maintain high pressure, low friction, point contact between saifd second conductor and said contacts, said point contacts and sai-d bearings rotatably mounting said first conductor on said second conductor and comprising the sole connection of said conductors.

6. In a side break switch having a rotatable insulator, a switch blade carried by the insulator and a terminal pad to be supported for rotation with respect to the insulator and bla'de and to be electrically connected to the blade, the improvement comprising fthe provision of a terminal pad having a bifurcated end portion, the bifurcations of said pad extending generaily perpendicular to the axis of rotation of the insulator and having aligned apertures therethrough aligned with the axis of rotation of the insulator, said terminal pad including a pad lug formed integrally with said bifurcated end portion for direct connectlon to a line, a tubular switch blade extending perpendicular to the axis of rotation of the insulator and including an end portion projecting over the insulator between and parallel to the bifurcations of said pad, a bracket secured to said blade in spaced relation to said end portion and connecting `said blade tto the insulator, said end portion of said switch blade being relatively thick and having a bore therethrough aligned with the axis of rotation of the lnlsulator and the apertures in the bifurcations of said pad, an nnperforate bar secured in said end portion of said blade in the region of said bore to define thereby a pair of aligned bores in the vopposite sides of said blade, a pair of silver contacts on opposite si-des of said bar each disposed in the bottom of one of said pair of bores, a cylindrical contact mounted in the aperture in each bifurcation of said pad, said cylindrical contacts being freely positioned respectively in said bores in said blade and each having a convex outer end engaging the respective silver contact solely at a point aligned with the axis of rotation of the insulator, each of said cylindrical contacts having a circumferential groove in the portion thereof positioned in Ithe respective bore, a plurality of ball bearings positioned in the groove in each cylindrical contact and bearing against the cylindrical Wall of the respective bore rotatably to mount said cylindrical contacts in said bores, a seal for each of said bores including an annular spring disposed between the respective bifurcation of said pad and the cylindrical contact mounted therein and the adjacent surface of said blade surrounding the adjacent bore to close the bore and seal the cylindrical contact and the ball bearings therein, a headed tie rod extending between and through said bifurcations of said pad in spaced parallel relation to the axis of rotation of the insulator and References Cited in the ile of this patent UNITED STATES PATENTS 2,227,925 Cornell et all Jan. 7, 1941 

